The invention lies in the nuclear power generation field. Specifically, the invention relates to a measurement device for determining the boron concentration in the coolant of a cooling circuit of a nuclear power station.
Boron is used as a neutron absorber in the coolant of the cooling circuit of a nuclear power station. The boron serves to control and compensate for the consumption of the fuel rods since neutrons are absorbed, i.e. removed from the chain reaction, to a greater or lesser extent depending on the boron concentration. Irregularities in the power density distribution due to otherwise customary mechanical control components can therefore be avoided, with the result that performance can be improved. It is consequently necessary for the boron concentration in the coolant, in particular in the coolant of the primary circuit or in auxiliary circuits, to be monitored.
It has become known from the document xe2x80x9cKernenergiexe2x80x9d [nuclear energy], vol. 11, 1967, p. 337-39, to determine the boric acid concentration with a method that involves measuring neutron absorption. The measurement device used there allows a determination of the boric acid concentration under normal operating conditions, i.e. up to an ambient temperature of 120xc2x0 C. and a system pressure of 120 bar. Cooling circuits of nuclear power stations, however, and in particular the primary circuit, are often subject to temperatures of up to 380xc2x0 C. with a system pressure of about 180 bar. Because of those system conditions, which are more severe than normal operating conditions, the measurement device described in the document is used in monitoring modules, at a sufficiently great distance from the cooling circuit.
In that that prior art measurement device, intervention in the cooling circuit is necessary. A bypass line branching off from the cooling circuit passes through the measurement device in order for the boric acid concentration to be determined. The use of a measurement device of that type, which is designed as a continuous-flow meter, is limited in terms of its mobility. The assembly is very expensive and leads to fairly long outages of the nuclear power station.
It is accordingly an object of the invention to provide a of the invention is therefore to provide a measurement device for determining the boron concentration in the coolant of a cooling circuit of a nuclear power station, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which makes it possible to measure the boron concentration without intervention in the cooling circuit and in a particularly simple way.
With the foregoing and other objects in view there is provided, in accordance with the invention, a measurement device for determining a boron concentration in a coolant conducted in a coolant-carrying component of a coolant loop of a nuclear power station. The device comprises a mobile emitter adapted to be disposed on the coolant-carrying component with a coolable space formed in between, and a mobile receiver adapted to be disposed on the coolant-carrying component with a further coolable spaced formed in between.
In other words, the invention provides for a mobile measurement device which includes a mobile emitter and a mobile receiver which are respectively placed, with the interposition of at least one coolable space, on the coolant-carrying component of the cooling circuit.
The basic concept of the invention is that, instead of a bypass line for a continuous-flow meter, part of the cooling circuit system itself can be used for the measurement. The measurement device is preferably constructed in such a way that it can be fastened directly on the cooling circuit. It is in this case particularly insensitive to temperature and radiation. In this regard, it may also be used under extreme ambient conditions.
In accordance with an added feature of the invention, the coolable space is formed in a cooling duct through which a coolant flows. The coolant is preferably air and its temperature can be predetermined.
In order to make it possible to protect the emitter and the receiver from high temperatures of the component, it is favorable if a cooling duct through which a coolant flows is arranged on the component at least in the respective region of the emitter and the receiver. For example, the cooling duct may be arranged in the space between the emitter and the component, and in the space between the receiver and the component. In the present context, the term component includes, by way of example, a tank, a boiler, a piece of piping or another vessel, possibly with large surface area, which carries or contains the coolant.
In order to guarantee simple and efficient cooling, i.e. maximally constant and reliable cooling of the emitter and of the receiver, air is the preferred coolant. To this end, the air or cooling air is blown through the cooling duct, for example using a fan. Further, the temperature of the cooling air can expediently be defined in advance. The temperature then defined in advance guarantees that the cooling air does not pass above or below a limit value. To this end, for example, it is possible to control the cooling air flow by means of the power of the fan. This guarantees that all parts of the measuring instrument are protected against overheating.
The one or two regions of the emitter and the receiver also advantageously have an insulation layer which is arranged, for example, directly on the component of the coolant circuit. In the insulation layer, air is for example used as insulator. The emitter and the receiver are preferably respectively arranged in an associated chamber. This provides spatial separation, by means of which the emitter and the receiver are respectively accommodated while being protected against excessive temperature.
The boron concentration is best measured by measuring a degree of neutron absorption in the medium. For that purpose, a neutron source is used as the emitter and at least one counter tube is used as the receiver. For reasons of the radiation from the neutron source, and because of effects on the measurement by external factors, for example moisture, a shield is provided. The shield may be a common shield or individual shields for the neutron source and the counter tube. The shield expediently comprises a first layer of an absorbing moderator and a second layer of neutron-absorbing material, e.g. cadmium sheeting, as well as a third layer of austenitic material, e.g. steel sheeting.
By means of the absorbing moderator, e.g. polyethylene moderator, the neutron flux produced by the emitter is slowed and partly reflected. Low radiation exposure for the operating personnel is therefore guaranteed, in particular through the use of the absorbing moderator and the cadmium sheeting.
In accordance with another feature of the invention, the emitter and the receiver are arranged in a casing made of one or more parts, in particular two parts. To this end, for example, the emitter may be arranged in a first casing part and the receiver in a second casing part.
In order to make it possible to fasten the emitter and the receiver particularly straightforwardly and reliably on the component or the line segment of the coolant loop, at least the emitter and the receiver can be fastened using at least one fastening means on the component or on the line segment. To this end, for example, the two casing parts may be placed so that they engage on the line section and may be screwed together using the fastening means. In the case of components with large surface area, fastening may take place, for example, via support devices. On no occasion is the component from which measurements are taken damaged or compromised. Neither structural measures nor interventions on the component are therefore necessary.
Due to the fact that the measuring method involving neutron absorption is decisively dependent on the consistency of the measurement geometry, a number of spacers are provided such that the length of the measurement path between the emitter and the receiver is approximately constant even in the event of a change in the ambient conditions. This is applicable, of course, for a straight-line measurement path or a measurement path in which there is at least one reflection point. Spacers of this type, for example support devices, are expediently designed so as to be resistant to temperature and expansion. The term expansion-resistant as used in this context means that the material of the spacer has a small or negligible coefficient of thermal expansion within the relevant temperature range.
In accordance with again another feature of the invention, the emitter and the receiver are arranged at least approximately opposite one another on the component. This forms a straight-line direct measurement path. The straight-line path is favorable for components with relatively small structural dimensions. As an alternative, the emitter and the receiver may be arranged on the component in such a way that the measurement signal received by the receiver is essentially a reflection of the emitter signal, i.e., it is a reflected measurement signal. This design is appropriate, in particular, for components with large volume. It will be understood that the signal output by the emitter may be reflected one or more times.
In order to make it possible to represent the value of the boron concentration as a function of time independently of effects due to pressure, temperature and radiation, at least the receiver is connected to an evaluation unit. With the aid of model-based plausibility and balancing algorithms, it is possible to eliminate spurious effects so that an accurate representation of the measured values of the boron concentration in the medium is guaranteed.
The advantages achieved with the invention consist, in particular, in that, owing to the simple construction of the measurement device, in particular because of the mobility of the emitter and the receiver, no intervention in the cooling circuit of the nuclear power station is needed in order to determine the boron concentration. Further, the measurement device is configured by means of the coolable region such that it is suitable for use under extreme system conditions or operating conditions, for example up to operating temperatures of 380xc2x0 C. The measurement device is therefore suitable in particular for mobile use as well as for retrofitting existing stations.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a boron meter, i.e., a measurement device for determining boron concentration, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.